It is known that many pharmaceuticals are not stable against oxygen and water vapor and that some change occurs in about 40% of pharmaceuticals when they are left to stand in unpacked condition, thereby causing a fatal problem in the pharmaceutical quality. Therefore, most of the commercially available pharmaceuticals, especially solid formulations, are packaged with a packaging material such as PTP (press through pack) sheet and protected from oxygen and water vapor. In recent years, PTP sheets in which polyvinylidene chloride having superior water vapor barrier property (moisture resistance) and oxygen barrier property are laminated have been developed and put into practice.
As a method of improving the stability of a solid formulation against oxygen and water vapor, methods of sugar-coating the solid formulation and methods of film-coating the solid formulation with a macromolecular substance have been put into practice. In the latter film-coating methods, polyvinyl alcohols and sodium carboxymethyl cellulose are known as a macromolecular substance exhibiting oxygen barrier property, and as a macromolecular substance exhibiting water vapor barrier property, aminoalkyl methacrylate copolymer E (Eudragit EPO (registered trademark); Degusssa Co.) is known.
Recently, as a macromolecular substance having an improved oxygen barrier property, a resin composition obtained by copolymerizing a polyvinyl alcohol and a polymerizable vinyl monomer (WO 05/019286) and a coating material obtained by adding talc and a surfactant to a polyvinyl alcohol (JP 2006-188490 A) have been developed to try to improve the stability of solid formulations. In addition, in the field of packaging films, as a method of improving gas barrier properties (oxygen barrier property and water vapor barrier property) in high humidity, methods of dispersing an intercalation compound in a polyvinyl alcohol have been proposed (JP 11-315222 A and JP 9-150484 A).
Meanwhile, at medical sites and dispensing pharmacies, to prevent patients from forgetting to take their prescribed drugs or making mistakes in the dosage thereof, it is widely practiced to use single-dose formulation which is prepared by taking a plurality of pharmaceuticals to be taken at once out of the respective packaging material such as PTP sheet and provides them altogether in one bag.
However, in those pharmaceuticals used in single-dose formulations, although the stability against oxygen and water vapor is ensured by the packaging material such as PTP sheet at the stage when the pharmaceuticals are put onto the market, since they are stored in unpacked condition over a prolonged period at medical scenes and the like, there is a risk of causing a deterioration in the quality of the pharmaceuticals.
To avoid this risk, there is a method of sugar-coating a solid formulation. However, sugar-coating of a solid formulation not only requires a long processing time, but also makes the resulting solid formulation excessively large, rendering it difficult for patients to take. Consequently, there are currently limited cases where this method is applicable. In addition, at present, the existing methods of film-coating a solid formulation cannot allow the resulting solid formulation to exhibit sufficient oxygen barrier property in high humidity, and even when the resin composition according to WO '286 is used, the resulting oxygen barrier property falls short of that of a packaging material such as PTP sheet. In the field of packaging films, there are coating materials having superior oxygen barrier property. However, they cannot be applied to a solid formulation since they are laminated films with a substrate film.
In view of the above, it could be helpful to provide a coating material for a solid formulation which is capable of stably retaining the quality of the effective ingredient in the solid formulation for a prolonged period even in unpacked condition in such a manner that the solid formulation can be used in a single-dose formulation.